The present invention relates generally to heating, ventilation and air conditioning (HVAC) systems for hybrid vehicles, and more particularly to thermal storage for HVAC systems in hybrid vehicles.
Some hybrid vehicles do not have the capability to provide air conditioning comfort when the engine is off. To improve the overall fuel economy of the vehicles, however, it is generally preferable to have the engine off as often as possible. Nonetheless, not having continuous air conditioning capability may be unsatisfactory to vehicle occupants as compared to conventional vehicles where the engine runs all of the time—allowing for air conditioning whenever desired.
In order to address this concern, some have proposed systems for hybrid vehicles that provide air conditioning even when the engine is off. For example, some hybrid vehicles include refrigerant compressors that have their own electric motor to drive them so they can be driven independently of the engine. Others not only have a separate motor to drive the refrigerant compressor, but also incorporate a dual drive mechanism where the compressor can also be driven directly off of the accessory drive belt. However, both of these solutions add to the weight and cost of the vehicle due to the addition of the extra compressor motor as well as the electronics and cables to operate the motor. Still others have attempted to alleviate this concern by providing refrigerant thermal storage systems or secondary loop coolant system that allow for air conditioning comfort during engine off vehicle operation. But these systems still add significant cost to the air conditioning system, and some only provide the air conditioning comfort for limited amounts of time before the engine must be restarted. Moreover, the secondary loop systems have additional thermal mass that must be cooled. They also may incur intermediate heat exchanger losses or require separate fluid fill systems (e.g., coolant fill, refrigerant fill or other type of fluid).